Cyclobutadiene Rhodium Complexes as Catalysts for the Synthesis of Amides from Electron‐rich Arenes, Tosyl Azide and CO

Abstract

Cyclobutadiene rhodium complexes [(C4R4)RhX]2 (R=Et, Ph; X=I, Cl) at 0.5 mol % loading catalyze the formation of aromatic amides from various indoles, tosyl azide, and carbon monoxide (1 atm). The reaction gives good yields of the target products (typically 60–85 %) and tolerates both donor and moderately acceptor substituents in the indoles (alkyl, OMe, Hal, COOMe, but not CN). The DFT calculations at the PBE/3ζ level revealed a new plausible mechanism for the reaction of TsN3 with CO via cycloaddition and formation of RhCON3 metallacycle, which is more favorable than the commonly assumed formation of nitrene intermediate.

Catalytic activity of cyclobutadiene rhodium complexes in hydrosilylation and other transformations of alkynes

“…All products were isolated in air. 1 H and 13 C NMR spectra were measured with a Bruker Avance 400 spectrometer at 20 1C. Chemical shifts are reported in ppm using the residual signals of the solvents as internal standards.…”

“…1 H NMR (400 MHz, acetone-d 6 ) d: 7.47-7.32 (m, 30H, Ph), 1.50 (q, J = 7.5 Hz, 8H, CH 2 ), 0.99 (t, J = 7.5 Hz, 12H, CH 3 ). 13…”

“…Indeed we found that cyclobutadiene complexes catalyze reductive amination of aldehydes in the presence of CO, 11 insertion of diazo compounds into E–H bonds, 12 as well as formation of amides from TsN 3 , CO and arenes. 13 However, a number of the explored catalytic reactions remained limited and the direct comparison with well-known diene complexes was made only briefly. In this work we report the investigation of catalytic activity of cyclobutadiene rhodium complexes in several reactions, which are typical for their non-conjugated diene analogs, such as hydrosilylation of alkynes, 1,4-addition of boronic acids to cyclohexanone, and Diels–Alder reactions.…”

Cyclobutadiene platinum complex as a new type of precatalyst for hydrosilylation of alkenes and alkynes

“…[1,2] However, their catalytic activity has remained essentially unexplored until our first report in 2015. [3] Recent investigations have revealed that cyclobutadiene complexes of rhodium have similar reactivity to their diene congeners and can effectively catalyze the reductive amination of aldehydes by CO, [4,5] the synthesis of isocyanates from azides and CO, [6] and insertion of diazoacetates into EÀH bonds. [7] At the same time, the catalytic activity of cyclobutadiene complexes of other transition metals has remained mostly unexplored.…”